Method of producing chromium



June 20, 1933. w. ROHN 1,915,243

METHOD OF PRODUCING CHROMIUM Filed April 9, 1952 3 Sheets-Sheet 1 INVENTOR W/LHELM ROHN ATI'ORNEY June 20, 1933. w. ROHN METHOD OF PRODUCING CHROMIUM Filed April 9, 1932 3 Sheets-Sheet 2 INVENTOR W/LHELM ROI-IN ATTORNEY June 20, 1933. ROHN. 1,915,243

METHOD OF PRODUCING CHROMIUM Filed April 9, 1932 3 Sheets-Sheet 3 INVENTOR 3 W/LHELM ROHN BY q ATTORNEY Patented June 20, 1933 UNITED STATES PATENT'OFFICE WILHELM BORN, OF HANAU-ON-THE-HAIN, GERMANY, ASSIGNOR TO HERAEUS- VACUUMSCHMELZE A. G., OF HANAU-ON-THE-MAIN, GERMANY, A .GERMAN COM- IPANY METHOD OF PRODUCING GHROMIUM Application filed April 9, 1932, Serial 1T0.

This invention relates to the art of metallurgy andmore particularly to the production of chromium metal by the reduction of chromium oxide or ore by hydrogen.

Heretofore in the art it has been proposed to produce pure chromium by direct reduction of chromium oxide by hydrogen.

One process contemplates the reduction of chromium oxide in an externally heated tube through which hydrogen is passed; but this cannot be carried on at a temperature higher than about 1560 C. because this is the highest temperature which the tube will withstand and at whichit remains gas-tight. For this method of operation the tubes must be of quite small diameter, and consequently the rate of production would be very lim ited. The main drawback to this method, however, is that hydrogen will not reduce chromium oxide appreciably at 1560 0. unless it contains as little water-vapor as can be secured only by cooling the hydrogen to liquid air temperature. or these reasons this procedure is not economically feasible for the production of chromium.

One of the objects of the present invention is to provide an improved method of reducing chromium oxides to chromium metal.

Another object is to provide apparatus for the reduction of chromium oxide to chromium metal.

Other objects and advantages will be apparent as the invention is further disclosed.

In accordance with the objects of the present invention I have found that when the source of heat is arranged within a containing vessel in such a way that the vessel itself remains cool, one may readily make use of higher temperatures, up to and beyond' about 1750 C. the melting point of chromium and even beyond 2000 C. This increase of temperature is, I have found, highly advantageous in that chromium oxide at about 1700 C. is reduced by hydrogen dried by cooling it in the range to O., a range readily attained by the vaporization of a mixture of solid CO; with acetone, ether, trichlorethylene, etc., or of ammonia under reduced pressure; and the 604,814, and in Germany April 15, 1931.

cost of thus freeing hydrogen to this extent from water vapor is only 1/10 to 1/15 of the cost when cooling to liquid air temperature is re uisite. It is understood that another met od of drying the hydrogen as by absorption by P 0 or other drying agents 1s entirel equivalent to the freezing process describe A further economicadvantage is that with internal heating a containing vessel of any size may be used so that large charges of the oxide may thus be reduced in an atmosphere of hydrogen. For, this purpose one may use a heating element of molybdenum whichenables temperatures of 2000 C. to be attained and is perfectly stable in the atmosphere required for the reduction of the chromium oxide.

The necessary temperature can be still more advantageously reached and maintamed by inductive heating of metallic chromium, a small quantity of which is placed initially in the reaction chamber for this purpose. The chromium oxide is placed onthis chromium, the vessel is closed and the requisite hydrogen atmosphere is established within it, and the current is turned on; the metal'melts, reduction of the oxide begins, and the additional liquid metal so produced aids in the maintenance of the reqof a preferred type of induction heating fur-- nace useful in the present invention;

Fig. 2 is a cross-sectional plan view of the same along plane 2-2 of Fig. 1;

Fig. 3 is a second sectional side elevation view of the same taken along plane 3-3 of Fig. l;

\ing application.

Fig. 4 is a second cross-sectional plan view taken along plane 4-4 of Fig. 3;

Fig. 5 is a reduced sectional side elevation view of the same similar to Fig. 3 showing the associated reducing gas circulation and purifying apparatus schematically;

Fig. 6 is a sectional side elevation view of a modified furnace structure;

Fig. 7 is a cross-sectional view of the same; and

Fig. 8 is a sectional side elevation View of a second modified furnace structure.

Referring to the drawings, the preferred apparatus illustrates a furnace of the induction type which is specifically described and claimed in my copending application Serial No. 557.234 filed August 15, 1931. In this special type of furnace a low frequency current may be employed and the induced eddy currents produced by reason of the special coil design illustrated effects a stirring of the molten metal .bath within the furnace from the bottom to the top thereby promoting and accelerating the rate of reduction of the chromium oxide on the top of the bath as well as facilitating and accelerating the rate of absorption of the reduced metal within the molten bath.

The furnace structure disclosed by the drawings substantially includes a crucible 1 interiorly faced with refractory material and. a top 2 interiorly faced with refractory material and hermetically sealing the cucible 1 as indicated at 11, the hermetic seal being water cooled as indicated at 10. About the outer periphery of the crucible 1 are disposed a plurality of flat wound bowl shaped coils 3 substantially as indicated to conform with the contour of the peripheral face of the crucible as is more fully disclosed and claimed in my said above identified copend- A core 5 is supported by pin 12 in a rotatable bearing carried by a support 4 at opposite sides of the crucible 1, the pin 12 in support 4 also serving to reta-tably carry the entire weight of the crucible 1, top 2, coils 3 and core 5.

Crucible 1 is provided with two discharge openings as indicated in Figs. 3 and 4 each of which are normally closed by refractory elements 13 either of which are arranged to be readily removed when desired. Through the top 2 a gas inlet pipe 8 is providedv and through one of the discharge openings a gas outlet pipe 9 is provided. In the normal operation of the furnace ahead of pressure is maintained on the gas inflow such that the space enclosed within the crucible 1 and top 2 substantially filled with gas at all times.

In accordance with the hereinabove described method I may place initially a small quantity of chromium metal 6 in the bot-- tom of the crucible 1 and on the top thereof place the chromium oxide 7 which it is desired to reduce. The chromium oxide reduced by the hydrogen during a reduction run incorporates with the chromium metal originally added and gradually builds up a larger molten bath of metal within the crucible 1.

The combined apparatus of the present invention is more clearly illustrated in Fig. 5 wherein is shown the induction furnace of Figs. 1 to 4 inclusive cooperatively connected with the reducing gas circulating and regenerating system. The elements heretofore identified. with respect to the furnace structure and assembly are identified by similar numerals.

In Fig. 5 hydrogen of commercial purity is delivered to storage tank 40 through valve 79 wherein it is stored under pressure. From tank 40 it passes through valves and 76 and appropriate piping into chamber 20 wherein it passes over cooling coils 22 carrying fluids or gases cooled to temperatures approximating 60 to --70 C. as hereinbefore described. Baflle plates 30 insure circulation of the hydrogen over coils 22. The thus purified hydrogen then passes through valves 77 and 78 and appropriate piping to inlet pipe 8 directly into the furnace wherein it circulates over the chromium oxide 7 which has been heated by conduction and radiation from molten bath 6 to temperatures at least approximating 1700 C.

The hydrogen is expelled from the furnace through pipe 9 in a strong free flow and passes directly into a second cooling and purifying chamber 20 which may be substantially identical with the first chamber 20 wherein it is circulated similarly over cooling coils 22 and thence returned through valves 71 and 72 and appropriate piping to pressure pump 34 operated by motor 36 which pump forces the substantially urified gas back into storage tank 40 throng valves 73 and 74 and appropriate piping.

Cooling coils 22 in each purifying chamber 20 may be connected in series or in parallel as shown to refrigerating means 26 and a pump 24 should be provided to maintain circulation of the cooling fluid or gases therethrough. Chambers 20 should also be provided with suitable drain out means 28. substantially as indicated when coils 22 are defrosted.

Instead of using the type of furnace indicated in Figs. 1 to 4 inclusive, I may employ the type shown in Figs. 6 and 7, wherein a high frequency induction coil 108 with terminals 109 and 110 is used as a heating means. In such a furnace, container 100 preferably should be comprised of tubular or cylindrical non-metallic material such as glass quartz glazed porcelain and the like. Crucible 102 may be of the shape illustrated or may be made more bowl shaped and also should be comprised of highly refractory materials non-reactive with chromium metal 106. Chromium oxide 104 is superposed upon the metal 106 substantially as indicated and gas inlet means 8 and gas outlet means 9 are. provided substantially as llereinbefore disclosed. In this type of furnace, the solid piece of chromium metal 106 is first incandesce'd and melted by high frequency induction heating by coil 108 and the chromium oxide 104 is progressively reduced by the circulating free flow of hydrogen thereover substantially as hereinbcfore described. v

Referring to Fig. 8 a second modification of furnace structure suitable for the purposes of the present'invention contemplates the use of an incandescent heating element 120 instead of induction heating. By this means the reducing gas itself is heated to the requisite reducing 'temperatureand thereby by radiawall of tion and conduction the metal oxide 104 retained in refractory crucible 102. Heating element 120 may be comprised of molybdenum as hcreinbefore described and may be mounted substantially as shown with terminals 122 and 12-1 extendingthrough the container 100. Other methods of moigiting'heater 120 may be devised if desire lVhereas the present invention has been described with particularity in'connection with the use of substantially pure (moisture free) hydrogen as areducing agent it iszngt'ttf be considered as being limited thereto Ihave found that the reduction of the metal oxide may be effected also by substantially pure (moisture free) hydrogen in which there has been incorporated a proportion of carboncarrying gases such as hydrocarbon vapors, or

even by admixtures of coke oven gases, water gas and other such fuel gases in accordance with the invention disclosed and claimed in cop'ending application Serial No. 642,464 filed November 12, 1932. The effect of the carbon is to accelerate the rate of reduction but the amount of such carbon that is introduced in the gas must be so controlled that the resulting chromium is substantially free from carbon. It is to be understood that the present process involves the use of hydrogen substantially pure and free from moisture, but not necessarily excluding carbon-carryinjg gases insuch a limited proportion as will not permit the absorption of carbon by the metal.

The chromium produced in this way excels in purity other grades of chromium hitherto manufactured commercially; for

instance the chromium metal, as now prepared by the Goldschmidt process, contains varying amounts of aluminum and is otherwise not of constant composition.

Having broadly and specifically disclosed the present invention it is apparent that many modifications and adaptations may be made therein without departing essentially from the nature and scope thereof as may be "set forth in the following claims.

What I claim is:

1. The method of reducing chromium oxide with hydrogen which comprises heating the oxide to temperatures in excess of about 1600 C. and passing thereover a strong free flow of hydrogen previously purified by exposure to temperatures ranging from about 60 C. to about 70 C.

2. The method of reducing chromium oxide with hydrogen which comprises subjecting the oxide to the action of a strong free flow of hydro en heated to temperatures in excess of a out 1600 (1, said hydrogen having been previously purified by exposure to temperatures ranging from about 60 C. to about -7 0 C.

3. The method of producing substantially pure chromium which comprises superposing chromium oxide upon a molten metal bath comprised substantially of pure chromium, and circulating thereover a strong free flow of substantially pure hydrogen having a water vapor content substantially not in excess of that retained therein subsequent to exposure to temperatures approximating 60 C. to -70 C.

4. The method of producing substantially pure chromium which comprises forming a molten metal bath comprised of-substantially pure chromium, superposing thereon a 'quantity of chromium oxide and circulating thereover a strong free flowiofsubstantially pure hydrogen, said hydrogen having a water vapor content substantially equivalent to that obtainable by exposure of the gas to temperatures approximating -60 C. to 70 C.

5. The method of reducing chromium oxide which comprises maintaining the chromium oxide at a temperature in excess of about 17 C. and circulating thereover substantially pure hydrogen, said hydrogen having a water vapor content substantially equivalent to that obtained by cooling the gas to temperatures between C. and 7 0 C.

6. The method of producing substantially pure chromium which comprises forming a. molten metal bath comprised of substantially pure chromium, superposing thereon a quantity of chromium oxide, circulating thereover a strong free flow of substantially pure hydrogen having a water vapor content approximating that obtainable by exposure of the gas to temperatures approximating +60 C. to 0., and vigorously stirring the molten metal bath to facilitate the reduction of the said oxide by the said hydrogen and the incorporation of the resultant metal product in the said bath.

7. The method of producing substantially pure chromium which comprises forming a molten metal bath comprised of substantially pure chromium, superposing thereon a quantity of chromium oxide, vigorously stirring said bath by induced electric eddy currents and circulating thereover a strong flow of substantially pure hydrogen, said hydrogen havin a water vapor content substantially equlvalent to that obtainable by the exposure of the gas to temperatures approxi- 5 mating 60 C. to 70 C.

In witness whereof, I have hereunto signed my name.

WILHELM ROHN. 

